Method of forming a hollow core plywood door



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l J. J. WALDHERR 2,668,788

METHOD OF FORMING A HOLLOW CORE PLYWOOD DOOR 2 sheeis-sheet 1 IN VEN TOR.` Josep/z J Wald/zeri; By .9

Feb. 9, 1954 4 Filed Dec. 16, 194s Feb. 9, 1954 J. J. WALD'HERR METHOD OF FORMING A HOLLOW CORE PLYWOOD DOOR Filed DGO. 16, 1948 2 Sheets-Sheet 2 MyW# wlw/Md@ Patented Feb. 9, 1954 METHOD OF FORMING A HOLLOW CORE PLYWOOD DOOR Joseph J. Waldherr, Marshfield, Wis., assignor to Roddis Plywood Corporation, Marshfield, Wis., a corporation of Wisconsin Application December 16, 1948, Serial No. 65,677

4 Claims.

This invention relates to hollow core plywood doors and panels, and has for its principal object a new and improved structure of this type and a new and improved method of forming the same.

It is a main object of the invention to provide a method of making a hollow core plywood door or panel, utilizing waste saw lumber in the formation of the core.

Another object of the invention is to provide a new and improved hollow core plywood door or panel, the core of which is composed of waste saw lumber.

Another object of the invention is to provide an economic process for utilizing waste saw lumber in the formation of hollow cores or doors, panels and the like.

Another object of the invention is to provide a core for hollow core doors and the like, which, though composed of waste or scrap saw lumber `of random length, is strong and not subject to warping or shrinkage.

Further objects of the invention not speciiically `mentioned here will be apparent from the detailed description and claims which follow, reference being had to the accompanying drawings in which a preferred embodiment of the invention is shown by way of example and in which Fig. 1 is a plan view of a door containing the core of the present invention, with parts broken away the better to show the construction;

Fig. 2 is a cross sectional View taken substantially along the line 2--2 of Fig. 1, looking in the direction of the arrows;

Fig. 3 is a plan view of the core assembly jig;

Fig. 4 is a cross sectional view taken substantially along the line 4-4 of Fig. 3, looking in the direction of the arrows;

Fig. 5 is a plan View, partly diagrammatic, illustrating the press assembly frame; Fig. 6 is an elevational view showing the press assembly frame between the platens of a press;

Fig. 7 is a diagrammatic View illustrating a step in the process of forming the core; and

Fig. 8 is a diagrammatic View illustrating another step in the process of forming the core.

Hollow core plywood doors usually consist of a rectangular outer frame of saw lumber of the same characteristics as the facing panels of the door, between the inner edges of which frame are core members most generally composed of lumber sawed and fitted together to form a plurality of closed cells extending between the facing panels of the structure. These prior art structures, while generally quite satisfactory from a weight and wearing quality standpoint, are expensive to build because of the numerous exacting operations required in the formation of the core.

There accumulates around a plywood mill a considerable quantity of scrap veneer, and in the co-pending application of Matthew Gr. Faussner, Serial No. 765,777, filed August 2, 1947, now Patent lNo. 2,622,999, there is disclosed a method of utilizing such waste material in the formation of hollow core doors, panels and the like.

There also accumulates around a plywood mill a substantial quantity of scrap saw lumber which has heretofore been burned as waste. The present invention seeks to utilize such waste saw lumber in the formation of hollow cores for doors, panels and the like.

In the prior art of which I am aware, numerous efforts have been made to utilize random length Waste saw lumber in the formation of solid cores for doors, panels and the like, with considerable success; however, previous efforts to utilize such Waste material in the formation of hollow core doors, panels and the like, have not been too successful for the reason that the labor involved in utilizing such material in the formation of the structure has been so great that the final cost of the structure has been prohibitive. The present invention solves this problem by providing a process which utilizes waste saw lumber in the formation of cores for hollow doors with a minimum of labor, thereby keeping the cost of the finished product at a reasonable figure.

In the working up of the waste material to form core blocks for the doors, the random lengths of waste saw lumber are first cut to uniform dimension in any preferred manner, such as by a gang saw, and the individual blocks thus formed run through a stickling machine which finishes the blocks to uniform width and height accurate to Within very close limits. If desired, by providing the sticking machine with suitable cutters, grooves can be cut into the side of the blocks to give them essentially I cross sections, thereby to reduce the weight of the blocks and consequently the weight of the finished door or panel. The blocks so formed are laid up into a desired core pattern in a suitable jig adjacent the press in which the doors are to be finished. The pattern so formed and the jig are subsequently registered with a door frame laid up in the press frame and dropped into place thereon in a minimum of time, so that the operations of removing a nished door and laying up the parts for a succeeding door in the press frame can readily be accomplished within the curing time of the press so that the promaple, etc., and the inner plies of which areA acheaper wood selected for strength. The twoface panels of the door are spaced apart by a hollow rectangular frame consistingA of side rails extending from end to endof'" the door', and end rails abutting the inside faces ofl the sifderails` and extending therebetween. The side and endk rails are preferably composed of the same wood as the facing panels, although other woods may be used if desired. Within the hollow-'rectangle so formed are reinforcing members which abut against' the inside edges of the end rails, and. lock blocks which provide solid wood'into which locks and latches may bemortisedinthe usualim'anner. The lock blocks are spacedy withinl the door b'y supporting members abutting thereagainst and against the endirails.

Fitted in between the hollow rectangle so formed are the core blocks laid in spaced-apart relation, with the longitudinal median lines of the individual blocks extending transversely of the door. Alternate rows of blocks contain. two or more individual` blocks in substantial' alignment longitudinally,with.the outerr ends of these blocks abutting againstor in closeproximity to the inner edges of the supporting members ofthe framework. Interveningr` rows of coreiblocks-v are disposed'v inwardlyof the sides of the' door and w-ith their ends overlapping but spaced' from the ends of the blocks-in the firstrows. This arrangement provides ample support for'the facing panel sections intermediate ofthe door frame with thel result thatthe door is strong'and-not Subj ect to warping or distortion.

Referring now tothe drawings inl moredetail, particularly Figs; 1 and 2', the doorwill be seen to 'be composed ofv a rst facing panel l, preferablyl of three-ply plywood; with they grain off the outer two layers-extending longitudinally of the door and the grain of the middle ply extending transversely thereof. Around the'L edges: of' this panel are side rails 2 and Ewhich extend from end to end of the panelv Il Fitted between and abutting against the innerl edges ofV said rails4 2 and 3 are end rails l1 which; with the side rails,

are preferably composed of' the same wood as "f the lowermost plyY in the facing panel Il.

Fitted*` alongside of the side rails- 2- andl3f, and abutting against the inner edges of t-helend-rails 4, are reinforcing rails 5 which may be` composed of any type of wood preferably selected for its strength and durability rather than for its ability to take nishes. Located againstV the inner edges of the reinforcing rails 5 are lock blocks Evwhich are positioned in the door anclheld with:respect to the end railsf4 by supporting railsl which abut against the lock blocks andthe end rails.

Fitted within the hollow rectangle so formed are a plurality of core blocks 8 which, in the example shown, are arranged in rows 9, each of which contains two coreblocks locatedwith their outer ends either abuttingl against' or in close proximity to the supporting rails 'Ll the rows 9 being spaced apart a substantial distance. Intervening betweenlthe rows 9 are rows: l0; which, inthe example shown', containa single core block disposed approximately midway between the rows 9 and with the ends of the block overlapping but spaced from the inner ends of the blocks in rows 9. All of the blocks in the core are of random length but of uniform height and Width. While two blocks are shown in alternate rows, with rows containing -asi'ngle block intervening; this particular pattern may bea modified Within the teachings of the invention and two or more individual blocks placed in each of the rows, preferably, howevenwith the ends of the 'block overlapping in substantially the manner shown.

Placed upon the frame and core so formed and glue'df tothe frame'members, lock blocks and core blocks, isa second facing panel Il, preferably identicalwith the rst panel I. After the structure soj formed has been pressed and subjected to heat to set the glue, the structure is solid and strong'and not subject to warpage or shrinkage. Doors constructed as shown weigh from thirty to.` thirty-uve poundsfor.' a` particular.' size; depending' upon the kindl ofi wo'od employed; `as contrasted with ninety` t`o`v ninety-five poundsl for a door of th'esamelsize' andoffth'e's'ame woodbut having a solidcore. A

InI the door illustrated; tliei core' blocksi are placed in' rows'extending transverselyfof.thefdbor, which is a preferred arrangement.` This-.arrangement is notvoff thelessence-off the present' invention, and the particularfpatt'erniin1w-liieli-1tlie core' blocks are arranged' is-s'ubject to variations Within the teachings of the invention.

In the'y formation' of theV doorjust'ldescribed, random lengthsy of waste sawl llurfibeif ofi varying width and thicknessa'redi'rst rieduce'd to blocks of substantially the same thicknessinan'y prelferred manner.' In Fig. "73 such a' blockf 201 isbeing shown as' passingithrough as gangY sawI zi which producesuniform dirnen'silm;V random length, usable core blocks 252, and? smallerscrap members 23 which are discarded.' Whilev gang sawing as` illustrated' affordsalcheap; Vrapid method of formingthese blocks,- otherf arrangem'ents for' forming tliev same may be'l used"l within theteachingsiofftheinvention.'

Not aill ofthe waste lumber accumulated will be widelenough to'be cutinto'two-'lor more'usable `core blockA blanks-but rathermuch ofithiswaste will 'be of Such W'idthand.4r thickrles's.asvlo-permit performing' the next stepoff the process'L without anyv preliminary cutting. Altlioug-hl the core blocks: are fof random'4 length, theyl Inusty be short enough to fit between the-'frame ofthe door'and preferablyare slightlyless'f th'an li'alfi aslong as the.' distance' between the side members' of? the frame. Should the wastel include lumber' of greater length than can beusedfi it; will ofcourse, have to-be cut'intofshorte'r lengthl blocks before the blocks can be'assembled inthisfcoreipatternl; however, mostof the waste-'will' work` upf into usable length-blocks".

Individual? blocks so formed arei next fediv into a sticking machine: inf which cu-tters- 2&5 and 2-5 face` the fouredges of" thel block toL accurate dimension. Inj order toreduce the weightE of the core-blocks and' door in'theexampleshown; cutters 2-'5 are varranged to cut groovesk ZGinfthevsides of the block, git/ingI itessentially ani-If shapel in crosssection. Assliown; the greovesIZ-i-are semieircular; however, anydesiredf shape of* grooves may bei used or the grooves may: be omitted" entirely,l if 'desired The randcmi-l'engthcore blocks so formed are ready for assembly-'in the* core As will-ipe seen inf-ligs;y B'land A? Ii'havefp'rovidd a jig in which the core pattern may be laid up. As shown, this jig consists of a rectangular frame 30 which contains a slidable tray 3i and a plurality of spacers 32 which divide the frame into `a plurality of transversely extending slots or pockets. The inside width of the frame is preferably approximately the same as the core pattern, although, if desired, cores of varying widths may be laid up a single jig. Located in the pockets formed between spacers 32 and adjacent the center ci the jig are blocks 33 which space the core blocks in these pockets inwardly so that they `will nt between the lock blocks i in the door structure.

Fitted upon the one end and one side of the frame 30 are guide blocks B by which the frame is registered with a press frame, as will presently appear. Frame 3Q, spacers 32 and tray 3l, and the blocks 33 and 3d may all conveniently be formed of wood, preferably plywood, so that when a core pattern is laid upin the frame it will be suflciently light to enable it to be readily lifted and placed in registration with the press frame, as will presently appear.

The particular type ci press frame employed will, of course, depend upon the type of press being employed to clamp the structure and set the glue therein. In one instance, the platen of the press is twice as long as the press, with the result that one end of it projects from the side of the press to permit removing a completed door and laying up the parts oi the next door while the structure at the other end of the platen is being pressed and cured. In other presses, a plurality of platens and structures are stacked one above the other in face-to-iace relation and pressed and cured simultaneously. In either instance, a press frame such as is shown in Fig. 5 will be employed. This frame consists of a rectangular structure 4t, three sides of which are fixed and the fourth side il is movable and adapted to be forced towards the opposite side, as illustrated by the ram `t2.

In laying up a door structure, a facing panel, such as l, is glued on its upper face and laid Within the frame 40. Within the frame and on this panel, side rails 3, end rails 4, reinforcing rails 5, lock blocks 6, and supporting rails l' are laid in the positions shown and the frame then closed to move side il laterally, thereby to register side rails 3 against the end rails 4. The jig shown in Fig. 3 and core pattern laid up in it are then registered With the frame dil, being located thereon by engaging the blocks 34 with the outer edges of the frame on one side and at one end. The tray 3i, which forms the bottom of the jig, is then moved with respect to the frame 30 of the jig to open the bottom of the individual transverse pockets in the jig and permit the core blocks to drop onto the upper surface of the facing panel I and between the side blocks l and end rails ll of the door frame.

As shown, the tray 3i is adapted to move longitudinally of the frame to. In instances where it will prove more convenient because of space conditions around a press, the tray may be arranged to move transversely ofthe frame 30.

As soon as all of the core blocks have thus been deposited on the facing panel l, tray 3! is moved back into the frame 30 and the jig removed from the press frame for re-lcading. In the event that any of the core blocks, in falling out of the jig and onto the facing panel l, become misplaced, it is a simple matter for the operators to arrange them into the desired pattern. In most instances,

however, with the jig as shown, the core blocks will be properly placed and little or no arranging has been found to be necessary.

The other face panel li with glue on its lower face is then registered with the door frame and core members in the press frame l0 and the frame and contents moved into registration with the platens diagrammatically illustrated in Fig. 6 as 43 and 44, through which heat and pressure are applied to the assembly to set the glue and bind the individual parts of the door securely together. After the glue has been cured, the door is removed frcm the press and press frame and trimmed to accurate dimension and iinished in the usual manner, such as by sanding.

It has been found that the foregoing method produces high quality doors economically. One operator and a sticking machine can produce in excess of 10,000 feet of random length core blocks in an eight-hour day. One lay-up operator having two lay-up jigs can lay up cores sufficiently rapidly to have a completed pattern ready in the jig each time the press frame is available for re-loading. In one instance, utilizing an electronic press which cured and set the glue in approximately one minute, this one operator had no diiculty in laying up core patterns for one-half of the doors being cured in the press, the other side of the press being utilized to cure doors of a different pattern. One press crew of five operators kept the press busy with a minimum of lost time in changing from one end of the platen to the other, laying up in the press frames one or the other type of doors during approximately one minute curing time of the press.

Waste saw lumber, which is in small pieces of random length but otherwise perfectly good sound lumber, is utilized by the process of the present invention to form cores for doors rather than as fuel in the boiler plant. The labor involved in transforming the waste material into useful articles is sumciently low to keep the total cost of the finished product at a reasonable gure. The process requires a minimum of special equipment and a minimum of skill on the part of the operators.

Throughout the foregoing description, I have referred to the articles as doors. hollow cores for panels and the like may be made in the same manner and I am not to be limited to the doors described by way of example.

While the steps of the process have been outlined in detail, this has been done by way of example only, as there are many modifications and adaptations which can be made by one skilled in the art within the teachings of the invention.

Having thus complied With the statutes and shown and described a preferred embodiment of my invention, what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims.

What is claimed is:

1. rihe method of utilizing waste saw lumber in the construction of hollow core plywood doors which comprises: forming from said waste saw lumber random length blocks of essentially I section and of uniform height and width; arranging a plurality of said blocks in spaced apart relation in a core pattern; laying up a door frame on the upper face of a plywood facing panel that has glue applied thereto; registering said plurality of core blocks in said pattern within said frame and depositing the blocks upon said panel; placing a second facing panel that has glue on one face on said frame and core Obviously .y

- blocks `with the glue face engaging the frame tudinal median lines: of the blocksy extend trans versely-of thel core and in whichv the individual blocks are spaced apart longitudinally and'transversely'in the core; laying up a, hollow rectangular door frame on theupper` glued face` of a ply- Wood facing panel; registering said" core pattern with said frame and depositing the pattern. on the panel within the frame; placing over said frame and core blocks a .second plywood facing panel which has glue on its lower face; and clamping and heating said assembly to cure the gluel and thereby'bond the doorpartstogether;

3. The method of forming a hollow core plywood door from random length core blocks which comprises: laying up-the core blocks in substantially parallel, spaced-apart rows, with the ad'- jacent ends ofthe blocks in one row overlapping the endsy of-'the blocks inthe adjacent rows; laying up on the face of aplywood facing panel, to the upper face' ofwhich. glue has been applied, a hollow rectangular frame having outside dimensions substantially the same as the panel; registering the laid-up core blocks with said frame; dropping the core blocks intoi position within said frame and on said' panel; placing a second ply-wood facing panel, to the lower face of which glue hasbeen applied, over said frame and core blocks; clamping' the assembly; and subjecting lthe clamped assembly toheat to set the.` glue.

4. The method of forming hollow core plywood doors which comprises: cutting random lengthscrap saw lumber Vto. uniform height and width.; laying up said core blocks insubstan'tial- 1y parallel, spaced-apart rows, with adjacentends of the blocks in one row overlapping the ends of` the blocks in the adjacent rows; placing a panel of.l facing plywood that has. glue on one face, gluetface up, laying up on said panel a door framey having outside dimensions substantially the same as theY panel;l placing .saidlaid up core blocks on the glued face of said panel within said frame; moving the outerl ones of said. core blocks into substantial :abutmenty with the` inside edges of said doorv frame; registering asecond facing panel ywhich has gluev on its. lower face with said door frameV and core blocks; and applyingheatand'pressure to the assembly tocure the glue and thereby bind the parts together.

vJOSEPH J. WALDHERR.

References Cited in the le of' this patent UNITED STATES PATENTS Number Name Date 1,911,374 Loetscher May 30, 1933 2,073,896 Loetscher Manl', 1937 2,191,070 ConeV Feb. 20, 1940 2,243,022 Thomas May 20, 1,941 2,302,487 Beiger et al .Nov. 17:, 1942 2,385,352 Davis Sept. 25, 1945 2,401,281 Webb v May 28, 1946 2,479,870 Rundquist Apr. 23, 1949 2,531,375 Delegard et al Nov. 21., 1950 

1. THE METHOD OF UTILIZING WASTE SAW LUMBER IN THE CONSTRUCTION OF HOLLOW CORE PLYWOOD DOORS WHICH COMPRISES: FORMING FROM SAID WASTE SAW LUMBER RANDOM LENGTH BLOCKS OF ESSENTIALLY I SECTIONA ND OF UNIFORM HEIGHT AND WIDTH; ARRANGING A PLURALITY OF SAID BLOCKS IN SPACED APART RELATION IN A CORE PATTERN; LAYING UP A DOOR FRAME ON THE UPPER FACE OF A PLYWOOD FACING PANEL THAT HAS GLUE APPLIED THERETO; REGISTERING SAID PLURALITY OF CORE BLOCKS IN SAID PATTERN WITHIN SAID FRAME AND DEPOSITING IN SAID PATTERN WITHSAID PANEL; PLACING A SECOND FACING PANEL THAT HAS GLUE ON ONE FACE ON SAID FRAME AND CORE BLOCKS WITH THE GLUE FACE ENGAGING THE FRAME AND BLOCKS; AND CLAMPING AND HEATING SAID ASSEMBLY TO CURE THE GLUE AND THEREBY BOND THE DOOR PARTS TOGETHER. 